The invention relates to a drilling tool in accordance with the preamble of claim 1. A drilling tool of this kind is known, for example, from EP 1 230 058, which is likewise attributable to the applicant. In the region of the drill point of a drilling tool of this kind, two or more major cutting edges are connected to one another by a chisel edge. The practice of reducing the size of this chisel edge by applying a “thinned region” is known in the area of machining technology in general and from the abovementioned EP 1 230 058, in particular. Since the cutting rate is equal to zero in the region of the chisel edge, the mechanical load on the drill point of the drilling tool is significantly reduced by such a reduction in the size of the chisel edge.
In the production of drilling tools, the thinned region of the chisel edge is generally produced in a multi-stage grinding process. In a first grinding operation, the chip flutes and, if appropriate, the minor cutting edges provided at the boundary of the chip flutes are ground into the drilling tool blank. In a second process step, the major cutting edges, the chisel edge and the flanks adjoining the major cutting edges are ground. In a third grinding operation, the chisel edge is then thinned. For each grinding operation, the grinding tool, which is generally formed by a rotating grinding disk, is in each case applied again to the drill blank to be ground in order to grind the major cutting edges and the chisel edge, to grind the thinned region and to grind the spiral flutes. Each new application of the grinding tool to the drill blank entails the formation of discontinuities during grinding, thereby giving rise to unwanted ridges on the finished drilling tool.
These ridges must either be smoothed and removed afterwards by complex and costly finish machining processes. If such finish machining is omitted, the accuracy of running of the drilling tool may be impaired, and the mechanical loads acting on the drilling tool during the drilling operation increase, and this inevitably leads to a reduction in the life of the drilling tool.
EP 1 230 058 has disclosed a process for grinding a drill point which prevents the formation of ridges in the region of the drill point of the drilling tool disclosed there. The disadvantage with this grinding process is the fact that it is suitable only for the way, shown there, of grinding the drill point in the region of the chisel edge.